Due to high demands in fuel efficiency of a vehicle and more strict regulations of exhaust gases, demands for environmentally-friendly vehicles have been increasing, and hybrid vehicles have been provided as a practical alternative in response thereto.
As a power source, an engine and a motor are applied to the hybrid vehicle, and depending on driving conditions, features of the engine and the motor are embodied to provide fuel efficiency and reduction of exhaust gas.
The hybrid vehicle may provide an optimal output torque depending on how two power sources consisting of the engine and the motor are harmoniously operated.
The hybrid vehicle generally starts by driving the motor, under a condition where a state of charge (SOC) of a battery cannot generate a motor torque sufficient enough to start the vehicle, the engine is turned on to be controlled in an idle state, and then an engine clutch is engaged to start the vehicle with an engine torque that is transferred through the engine clutch.
In this case, when the torque transferred through the engine clutch, which is an assumed model value based on a current hydraulic pressure output, is different from the real torque due to disturbances including a kiss-point of the engine clutch, a friction coefficient, a load, oil temperature, etc., it has an adverse effect on operating ranges of the vehicle.
As a method for correcting characteristics of the engine clutch, a technology is provided in which experimentally acquired friction characteristics of the engine clutch are inputted as a friction coefficient to estimate a transfer torque, and when input and output revolution per minutes (RPMs) of the engine clutch are estimated, and the estimated RPMs differ from set RPMs, a closest characteristic curve actually generated in an characteristics map is selected to correct the friction characteristics.
The above characteristics correction method may have errors with a real transfer torque in selecting the characteristic map, and may have difficulties in dealing with an operation time delay of a hydraulic pressure rather than the friction characteristics of the engine clutch and the like.
Further, it is difficult to take differences of the respective engine clutches into account, and may cause a problem that the motor must be operable to estimate friction characteristic variation of the engine clutch.
As a learning method of a kiss-point (i.e., a real working pressure of the hydraulic pressure), a technology is provided in which an engine at deceleration maintains a fuel-cut control in an electric vehicle (EV) mode, the hydraulic pressure is applied to an engine clutch, and the time until which the engine speed is generated is measured. The measured time is compared with a predetermined target time, and a correction hydraulic pressure is calculated according to a time difference. The learned initial hydraulic pressure is subtracted by the calculated correction hydraulic pressure such that it is updated to be stored, and the updated and stored initial hydraulic pressure is applied when the engine clutch is combined.
The above method is a technology for defining an offset hydraulic pressure to generate the real transfer torque of the engine clutch, and hydraulic pressure characteristics should be considered in determining an amount of learning, and thus, the amount of learning may be dependent on driving conditions, thereby being unable to provide learning control according to load variation.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.